Internal combustion engines such as gasoline engines, diesel engines, and gaseous fuel-powered engines exhaust a complex mixture of air pollutants. In an effort to reduce the potential negative effects of these pollutants on the environment, exhaust emission standards for these engine systems have become more stringent. In fact, many industrialized countries impose environmental regulations that limit the amount of pollutants emitted to the atmosphere from an engine, depending on the type, size, and/or class of engine.
In an effort to reduce gaseous emissions, an emphasis has been placed on using electrical power to operate various components associated with a vehicle. Hybrid vehicles have been developed, for example, that rely on a combination of electrical energy and energy produced by a power source (e.g. an internal combustion engine or a fuel cell) to power certain electrical accessories such as, for example, traction motors for maneuvering the hybrid vehicle. Another example of such an electrical accessory includes a hydraulic motor for use with heavy duty equipment such as, for example, an implement. Further, hybrid vehicles typically include one or more power storage devices (e.g. batteries) to receive and store excess electrical power from the power source and/or electrical power from regenerative dynamic braking of traction motors.
With the inclusion of power storage devices as alternate sources of electrical power, new electrical system architectures are being developed to make use of the power storage devices to increase the convenience, fuel economy, and safety of hybrid vehicles. For example, power storage devices may be configured to power the traction motors and/or electrical accessories for a limited period of time without requiring use of the power source. Thus, these architectures may reduce or eliminate fuel costs and emissions associated with the use of the power source during the limited period of time. Further, because start-up of a power source can take a relatively long period of time (e.g. five minutes for some heavy-duty hybrid vehicles), these architectures increase vehicle productivity by powering systems of the vehicle during the start-up period, thereby reducing equipment downtime during start-up.
One example of a system that provides power to accessories in a hybrid vehicle without requiring start-up of a main power unit is disclosed in U.S. Patent Application Publication 2007/0103002 (“the '002 publication”) by Chiao et al. Specifically, the '002 publication discloses a heavy-duty hybrid vehicle power system including a main power unit, a power source (e.g. batteries, ultracapacitor packs, and/or flywheels), an electric propulsion motor, an electric accessory motor, and a DC-DC converter to step high voltage DC power down to a level required by low voltage accessories. The main power unit provides more than 42 volts of power to a DC power bus and is configured to provide power to the power source, the electric propulsion motor (via a first inverter), and the electric accessory motor (via a second inverter). The power source stores power from the main power unit as well as power generated from dynamic electromagnetic braking regeneration. The first inverter converts DC power from the DC power bus to AC power, which drives the electric propulsion motor to propel the heavy-duty hybrid vehicle. Similarly, the second inverter converts DC power from the DC power bus to AC power, which drives the electric accessory motor. The electric accessory motor powers a belt drive assembly, which drives one or more vehicle accessories. When the main power unit is shut down, the power source supplies DC power to the first inverter and the second inverter, thereby providing power to the electric propulsion motor and the electric accessory motor.
While the system of the '002 publication may provide power to an electric propulsion motor and an electric accessory motor without operating a main power unit, it may be inflexible. In particular, because the electric propulsion motor and the electric accessory motor are connected to the same DC power bus as the main power unit, the DC voltage delivered to the main bus is limited to the voltage output of the main power unit. As a result, changing the voltage output of the main power unit may necessitate changing the propulsion motor and accessory motor to comply with the voltage output of the main power unit.
Further, because the propulsion motor and the accessory motor are each limited to the voltage output of the main power unit, options for changing the propulsion motor and/or the accessory motor may be unnecessarily limited. For example, upgrading to smaller, lighter, more efficient high voltage motors may require a user of the hybrid vehicle to also upgrade the main power unit to provide the necessary output voltage. Thus, such an upgrade may be expensive.
The system of the '002 publication may further be inefficient because the power source may be connected to the same DC power bus as the DC-DC converter. That is, when the power source provides power to the accessories via the DC-DC converter, a portion of the power from the power source may be lost by the DC-DC converter, thus discharging the power source at an undesirably high rate. More specifically, the DC-DC converter may introduce power losses into the system when converting the DC power from the power source. As a result, the power source may discharge faster than if it were connected to power the accessories directly at a voltage appropriate for the accessories.
The disclosed electrical system architecture is directed to overcoming one or more of the problems set forth above.